T. Padmanabhan

Cosmological constant—the weight of the vacuum

Recent cosmological observations suggest the existence ofa positive cosmological constantwith the magnitude � (G˝=c 3 ) ≈ 10 −123 . This review discusses several aspects ofthe cosmological constant both f rom the cosmological (Sections 1- 6) and .eld theoretical (Sections 7-11) perspectives. After a brief introduction to the key issues related to cosmological constant and a historical overview, a summary ofthe kinematics and dynamics ofthe standard Friedmann model ofthe universe is provided. The observational evidence for cosmological constant, especially from the supernova results, and the constraints from the age of the universe, structure formation, Cosmic Microwave Background Radiation (CMBR) anisotropies and a few others are described in detail, followed by a discussion of the theoretical models (quintessence, tachyonic scalar .eld, :::) from di4erent perspectives. The latter part of the review (Sections 7-11) concentrates on more conceptual and f aspects ofthe cosmological constant like some alternative interpretations ofthe cosmological constant, relaxation mechanisms to reduce the cosmological constant to the currently observed value, the geometrical structure ofthe de Sitter spacetime, thermodynamics ofthe de Sitter universe and the role of string theory in the cosmological constant problem. c

Accelerated expansion of the universe driven by tachyonic matter

It is an accepted practice in cosmology to invoke a scalar field with potential

Thermodynamical aspects of gravity: new insights

V(\phi)

Gravity and the Thermodynamics of Horizons

when observed evolution of the universe cannot be reconciled with theoretical prejudices. Since one function-degree-of-freedom in the expansion factor

Cosmology with tachyon field as dark energy

a(t)

Classical and quantum thermodynamics of horizons in spherically symmetric spacetimes

can be traded off for the function

Can the clustered dark matter and the smooth dark energy arise from the same scalar field

V(\phi)

Statistical mechanics of gravitating systems

, it is {\it always} possible to find a scalar field potential which will reproduce a given evolution. I provide a recipe for determining

Hawking radiation in different coordinate settings : Complex paths approach

V(\phi)

EQUIPARTITION OF ENERGY IN THE HORIZON DEGREES OF FREEDOM AND THE EMERGENCE OF GRAVITY

from